CBSE Class 10 Science 2019 · Paper 31/5/1 · Question 5(b)

Sodium hydrogen carbonate is the salt of a strong base, sodium hydroxide ($\text{NaOH}$), and a weak acid, carbonic acid (${\text{H}}_2{\text{CO}}_3$). Such a salt gives a basic solution (pH about 8; it turns red litmus blue), so ${\text{NaHCO}}_3$ is a basic salt. Conversion into washing soda: on heating, sodium hydrogen carbonate decomposes into sodium carbonate, $2{\text{NaHCO}}_3\stackrel{\text{heat}}{\to }{\text{Na}}_2{\text{CO}}_3+{\text{H}}_2\text{O}+{\text{CO}}_2$; recrystallising the sodium carbonate from water gives washing soda, ${\text{Na}}_2{\text{CO}}_3+10{\text{H}}_2\text{O}⟶{\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$.